1. Field of the Invention
The present invention relates to an integrated differential cascode amplifier.
2. Description of the Background Art
High frequency amplifiers are required for a variety of applications. For instance, high frequency amplifiers are used to amplify radio signals that are received or are to be transmitted. In addition, high frequency amplifiers are used in mobile telephones and radar systems. For many applications, it is sufficient for the amplifier to amplify only a small frequency band in the vicinity of an operating frequency. Such an amplifier is also called a selective amplifier. Examples of prior art amplifier circuits are the differential amplifier and the cascode amplifier.
An arrangement of two transistors as a cascode amplifier accomplishes the result that a Miller effect which occurs in transistors in a common emitter circuit is negligible, so that the frequency response of the cascode amplifier is independent of the base collector capacitance of the transistor in the common emitter circuit influencing the Miller effect.
A differential cascode amplifier is known from EP 1 480 333 A2, which corresponds to U.S. Pat. No. 7,109,793 for example. In addition, a negative feedback is disclosed wherein a first capacitor feeds the output of the first branch of the differential amplifier back to the input of the second branch of the differential amplifier. A second capacitor is connected to the output of the second branch and the input of the first branch of the differential amplifier for feedback. By means of the feedback, instabilities in the differential amplifier are reduced by limiting the frequency response.